Ever since the political vulnerability of this nation's largely foreign controlled petroleum sources became painfully obvious in the early 1970's, there has been an intensive effort devoted to the development of alternative energy sources and conservation of existing resources. In more recent years, the acute nature of the energy problem has been underscored by a growing public awareness of the related environmental questions.
To a large extent, efforts aimed at energy conservation and alternative energy generation have met with a large degree of success in such areas as the heating and cooling of structures, automobile efficiency and the like. More particularly, large advances have been made by designing hotter running gasoline engines, use of reflective glazing, impermeable construction barriers, solar heating and the like.
However, one technology which has largely failed to live up to its very promising expectations is the use of hydrogen for the generation of electricity. Generally, this technology involves the utilization of hydrogen in electrochemical combustion for the purpose of generating electricity. A device in which such a process is carried out is generally referred to as a fuel cell. Because the electricity is generated by the combustion of hydrogen with oxygen, the only combustion product involved is water vapor which is completely harmless to the environment. This may be compared to gasoline combustion which involves the release of hydrocarbons, carbon monoxide, and complex chemical species into the environment (along with the primary emissions, carbon dioxide and water vapor).
While it has been known that fuel cells offer many advantages as compared to other power sources, particularly in supplying power at remote locations (such as outer space or the like) and offer at least, in principle, limited service and maintenance requirements, various problems are presented by existing fuel cell technology. Nevertheless, perhaps the most advantageous fuel cell systems presently available (for certain applications, at least) are those which utilize a so-called ion-exchange membrane (IEM) electrolyte. Generally, in systems such as this, the electrolyte is embodied in the form of a synthetic polymeric material which acts as an electrolyte while still having the characteristic of being a solid body.
This type of system offers numerous advantages. For example, since the electrolyte phase is solid, no operational complications arise from migration of electrolytic material into adjacent regions of the fuel cell. At the same time, the system is mechanically stable and hardy under a wide variety of operating conditions. Moreover, such fuel cells have the ability to operate at or near room temperature and thus provide virtually instantaneous start-up. In principle, such systems offer the possibility that thermal management may be passively achieved, although practical implementation of this in a wide variety of designs may pose difficult design problems.
Notwithstanding the general advantageous of such IEM fuel cell systems, difficulty arises in that product water tends to accumulate as a liquid adjacent the cathode where it hampers proper cell operation. More particularly, the problem involves the fact that the electrode generally comprises compacted graphite fibers which have been rendered relatively hydrophobic. As water molecules are formed at the cathode, these molecules tend to migrate away from the interface between the cathode and the IEM. This leads to their migrating across the cathode, and they tend to accumulate on the side of the cathode opposite from the IEM. Insofar as the first spaces encountered on the other side of the cathode are the air conduits for feeding oxygen to the cathode, and since these fuel cells typically operate at or near room temperature, these conduits tend to become filled with water, thus impeding fuel cell operation. The result is that the channels can lose a large measure of their functionality and the flow of oxygen which should be supplied to the cathode's catalytic reaction sites can be greatly impaired. The result tends to be a serious degradation in fuel cell performance.
One possible approach to solving this problem is the use of a pump to continually flush the oxygen-conducting channels or conduits. If one were to consider the use of a pump (or blower) which blows air at a relatively high rate of speed through the channels, such a device would consume significant amounts of electricity, might provide only limited relief to the problem, and is likely to cause IEM inefficiencies by lowering the internal water content of the IEM.
In an effort to alleviate this problem, it has been proposed that treatment of the channel-defining plates adjacent the cathode with a material that renders them hydrophilic would readily result in wicking away of water before accumulations become serious. Such treatment is accomplished by coating the surfaces of the channels with colloidal silica. In principle, it was intended that the product water be caused to migrate across the channel-defining plate surface to the edges of the plates, where the water could be collected.
While this sort of approach did help the problem of product water accumulation in passive IEM fuel cells, difficulties still remain. For example, the applied colloidal silica, while it did provide a hydrophilic layer, was found to erode over time, resulting in premature failure of the fuel cell due to progressive loss in hydrophilicity. Failure can be accelerated due to the fact that such deterioration of the colloidal silica layer could cause a build-up of silica in the channels, thereby impeding operation of the system by interfering with access of air to the catalytic sites of the cathode.